Charbonneau E, Chouinard P Y, Tremblay G F, Allard G, Pellerin D
Département des Sciences Animales, Université Laval, Québec, QC, Canada G1V 0A6.
J Dairy Sci. 2009 May;92(5):2067-77. doi: 10.3168/jds.2008-1569.
Decreasing the dietary cation-anion difference (DCAD) by using anion sources before calving reduces hypocalcemia in cows at calving. Reduced DCAD from CaCl2-fertilized timothy hay achieves similar results, but the effects of feeding low-DCAD forage as silage have not been determined. The objective of this study was to evaluate the effect of low-DCAD timothy silage on dry cows. Six nonlactating and nonpregnant Holstein cows were used in a replicated 3 x 3 Latin square. Treatments were 1) control diet (DCAD = 232 mEq/kg of dry matter, DM); 2) low-DCAD diet using a low-DCAD timothy silage (LDTS; DCAD = -21 mEq/kg of DM); and 3) low-DCAD diet using a fermentation by-product (LDBP; DCAD = -32 mEq/kg of DM). Differences between dietary treatments were considered statistically significant at P < or = 0.05 and tendencies were noted when 0.05 < P < 0.10. Compared with the control, feeding LDTS tended to decrease DM intake (10.6 vs. 12.5 kg/d) and decreased urinary pH (6.15 vs. 8.18) as well as apparent digestibility of DM (67 vs. 69%). Blood pH (7.37 vs. 7.42), HCO3- (25.3 vs. 27.5 mM), and base excess (0.4 vs. 3.1 mM) were decreased, and blood Cl- (29.6 vs. 29.1 mg/dL) was increased. Apparently absorbed Na and Cl were higher and apparently absorbed K, P, and digested ADF were lower for LDTS compared with the control. Both LDTS and LDBP resulted in similar DM intake. Urinary pH tended to be higher (6.15 vs. 5.98) and percentage of digested DM was lower (67 vs. 70%) with LDTS compared with LDBP. Blood ionized Ca (5.3 vs. 5.4 mg/dL) tended to be lower and blood Cl- (29.6 vs. 30.1 mg/dL) was lower, whereas blood pH (7.37 vs. 7.33), HCO3- (25.3 vs. 21.5 mM), and base excess (0.4 vs. -3.8 mM) were higher with LDTS compared with LDBP. Apparent absorption of Na, Cl, S, and P, as well as apparent digestion of acid detergent fiber, neutral detergent fiber, and N were lower, and K, Cl, S, P, Mg, and N were less retained with LDTS compared with LDBP. Results confirm that low-DCAD timothy silage can be used to produce a compensated metabolic acidosis by decreasing the DCAD of rations served to nonlactating dairy cows.
产犊前使用阴离子源降低日粮阴阳离子差（DCAD）可减少奶牛产犊时的低钙血症。氯化钙处理的猫尾草干草降低DCAD也能达到类似效果，但饲喂低DCAD青贮饲料的影响尚未确定。本研究的目的是评估低DCAD猫尾草青贮饲料对干奶牛的影响。选用6头非泌乳、未怀孕的荷斯坦奶牛，采用重复3×3拉丁方设计。处理方式为：1）对照日粮（DCAD = 232 mEq/kg干物质，DM）；2）使用低DCAD猫尾草青贮饲料的低DCAD日粮（LDTS；DCAD = -21 mEq/kg DM）；3）使用发酵副产物的低DCAD日粮（LDBP；DCAD = -32 mEq/kg DM）。日粮处理间差异在P≤0.05时被认为具有统计学意义，当0.05＜P＜0.10时记录趋势。与对照相比，饲喂LDTS使干物质采食量有降低趋势（10.6对12.5 kg/d），尿pH降低（6.15对8.18），干物质表观消化率降低（67%对69%）。血液pH（7.37对7.42）、HCO3-（25.3对27.5 mM）和碱剩余（0.4对3.1 mM）降低，血液Cl-（29.6对29.1 mg/dL）升高。与对照相比，LDTS的表观吸收Na和Cl较高，表观吸收K、P和消化ADF较低。LDTS和LDBP的干物质采食量相似。与LDBP相比，LDTS的尿pH有升高趋势（6.15对5.98），消化干物质百分比更低（67%对70%）。血液离子钙（5.3对5.4 mg/dL）有降低趋势，血液Cl-（29.6对30.1 mg/dL）较低，而与LDBP相比，LDTS的血液pH（7.37对7.33）、HCO3-（25.3对21.5 mM）和碱剩余（0.4对 -3.8 mM）较高。与LDBP相比，LDTS的Na、Cl、S和P的表观吸收以及酸性洗涤纤维、中性洗涤纤维和N的表观消化较低，K、Cl、S、P、Mg和N的保留较少。结果证实，低DCAD猫尾草青贮饲料可用于通过降低非泌乳奶牛日粮的DCAD来产生代偿性代谢性酸中毒。
